We propose to study the problem of the genetical changes that take place in species in which the random extinction of local populations and the colonization of vacant habitats occur on the same time scale as the genetical changes within single populations. We will use laboratory populations of flour beetles, genus Tribolium, (1) to determine the effect of extinction, colonization, and dispersion on the rate and the extent of genetical differentiation of local populations; (2) to characterize the nature of the observed genetic differentiation in terms of additive and nonadditive factors; (3) to examine the effect of environmental variation on the differentiation of local populations; and (4) to determine the genetical, ecological, and environmental conditions under which group selection would be an effective mechanism for evolution in natural populations. We will use the empirical results of these studies to provide realistic estimates of several parameters of a quantitative genetics model derived in collaboration with Dr. Montgomery Slatkin of the University of Washington at Seattle. The underlying assumptions as indicated by the experimental studies will be varied and the model will then be applied to other systems to test the validity of our predictions. Our goal is to develop a theory that is sufficiently general that it can be applied to natural systems but also sufficiently realistic that the underlying assumptions of the model can be tested independently of the predictions. This work is a continuation of and represents a logical extension of our earlier work on these and related problems.